Electrophotographic printers include a plurality of printing modules each for transferring toner to a receiver. Each printing module includes an imaging cylinder on which a latent image is formed which is then converted to a visible by the deposition on toner particles. The imaging cylinder then either transfers the toner to a receiver or transfers to one or more intermediate cylinders which then transfers to the receiver.
Each imaging cylinder is driven by a motor whose rotation is transmitted to the imaging cylinder by transmitting members, such as gears and pinions. These transmitting members may have its shaft not rotating exactly in line with the main axis, commonly referred to herein as runout. The prior art discloses several methods for compensating for runout.
For example, U.S. Pat. No. 5,243,396 discloses a timing belt of the speed reduction drive train having a peripheral length which is selected from a range of values dependent on a preselected speed reduction ratio between the driven pulley and the driving pulley. Further, each one of the range of values is an integral improper fraction or integral multiple of the circumference of the driven pulley. Moreover, the driving pulley of the last pulley belt set coupled to the photosensitive member and a driven pulley prior to the last pulley belt set rotate n full rotations as the photosensitive member rotates from the image forming location to the image transfer location. In conjunction, every speed reduction ratio of all pulley belt sets prior to the last pulley belt set is an integer value.
U.S. Patent Publication No. 20100080626 discloses a digital electrophotographic printer for printing on a receiver. The printer includes a gear drive assembly having at least two gears. A first gear includes first gear teeth and a second gear includes second gear teeth, each of which drives a photoconductor in a separate print engine in which the first gear teeth and the second gear teeth are offset an by offset value, b. Two or more print engines share the drive assembly, each print engine having an imaging cylinder and a writer. A controller directs a relative gear position of the first and second gear in relation to the drive assembly so that the two gears are out of phase to minimize the appearance of drive assembly tooth related velocity variations.
U.S. Patent Publication No. 20100303504 discloses a multicolor imaging system having a plurality of photoreceptors on which electrostatic latent images are generated. A plurality of development units generate toner images based on the electrostatic latent images on the photoreceptors, respectively. A transfer unit includes an endless belt element onto which the toner images are transferred sequentially while rotated, and a belt drive element which rotates the belt element. A drive unit controls the transfer unit via the belt drive element based on a fluctuation in a rotary velocity of the belt element so that the belt element rotates at a constant velocity, and drives one of the plurality of photoreceptors together with the belt element. A toner pattern detector detects a toner pattern on the belt element, and an arithmetic unit calculates a periodic fluctuation in each of the photoreceptors from information detected by the toner pattern detector. A rotary position detector detects rotary positions of the photoreceptors, and a controller adjusts a phase difference in rotations of the photoreceptors based on information detected by the rotary position detector. A drive gear system includes a gear and the belt drive element, and a gear system for the photoreceptors other than the one photoreceptor, comprised of a gear and at least one phase adjusting gear having a same rotary cycle as that of the gear of the drive gear system to adjust the rotary velocity of the photoreceptors other than the one photoreceptor to fluctuate in a same cycle as that of the one photoreceptor.
Although satisfactory, theses prior art methods include drawbacks. U.S. Pat. No. 5,243,396 involve the use of adjusting belts and the like which includes a tradeoff of adding inherent tolerance inaccuracies into one portion of the system for adjusting another portion the system. U.S. Patent Publication No. 20100080626 adjusts the phase of two independent gears but does not address the inaccuracies in each gear assembly independently of each other. U.S. Patent Publication No. 20100303504 addresses a phase difference in rotation of “two” photoreceptors but does not address the inaccuracies in each photoreceptor independently caused by runout. The use of separate motors to control the motion of each imaging module results in redundant subsystem hardware and unnecessary cost. Similarly, encoders or other complex sensing systems to sense the positional errors in motion control systems are expensive and should be avoided where possible.
The present invention addresses the shortcomings of the prior art.